DNA to Protein Activity

Goal: Transcribe DNA into mRNA, translate codons into amino acids with tRNA anticodons, and explain how one base substitution causes sickle-cell hemoglobin.

Open the tool at thebiologylab.org/dna-transcription-translation/ · Connects to NGSS HS-LS1-1

What to do

1. Press “Start–stop demo”. Record the length, the number of amino acids and the stop codon shown under the diagram.
2. Press “β-globin (normal GAG)” and then “Sickle cell (GTG)”. Record the same three readouts for each, and compare codon 7 in the two chains of amino acids.
3. Under What did you paste?, choose DNA template strand, 3′ → 5′. Type TACGGACTT and write down the mRNA and the amino acids for question 5.

Record your results

Questions

1. The demo’s coding strand begins 5′-ATG GCC-3′. Write the matching mRNA and tRNA anticodons for these two codons, and name the amino acids.

2. How many codons does the 39-nucleotide demo contain, and why does its protein have only 7 amino acids?

3. Compare codon 7 of normal β-globin and of sickle-cell β-globin. What is the base change, and how does it change the protein?

4. The sickle-cell protein is still 14 amino acids long here. Why does a substitution change only one amino acid, while deleting one base would change every codon after it?

5. You typed the template strand 3′-TACGGACTT-5′. What mRNA and amino acid sequence did you get?

6. Challenge: valine is nonpolar, while glutamic acid is acidic and carries a negative charge. Suggest why this one change makes hemoglobin molecules stick together.

Free from Biology Lab · thebiologylab.org · HS-LS1-1: Explain how the structure of DNA determines the structure of proteins, which carry out the essential functions of life.